Aristolochic acid (AAs), a cancer-causing compound meeting almost all the definitions and criteria of carcinogenic materials, has been identified as a Group 1 carcinogen. This paper centered on the evaluation criteria for chemical carcinogen and molecular mechanisms involved in carcinogenesis. Taking aristolochic acid as a typical example, we summarized the latest research progress in this field in terms of concept development and addressed the following key questions: (1) Do we have to understand its mechanism of action when defining a carcinogen? What is the impact of carcinogenic mechanisms on carcinogen assessment? (2) Why is aristolochic acid classified as a Group 1 carcinogen? (3) What are the signatures of base substitution mutation? (4) Why does oral exposure to AAs more often cause urinary cancer? (5) What are the differences in metabolism and transport between kidney and liver, and what about their effects on AAs toxicity? We believe that the interpretation of key issues in modern toxicological evaluation of aristolochic acid will help us thoroughly understand and follow the international research guidelines, and provide molecular toxicological evaluation and classification on traditional Chinese medicine compositions. Regarding genotoxicity evaluation, a field that is often ignored, it would be necessary to systematically collect the relevant valuable evaluation and evidence in a scientific and rigorous way. This will provide references and guidelines for research evaluation of future cases similar to the AAs event.